1. Field of the Invention
This invention relates to a composition forming an elastic polyorganosiloxane foam with evolution of hydrogen gas at room temperature, and more particularly to a polydiorganosiloxane composition having a practically sufficient and adequate pot life and being capable of forming an elastic form which exhibits a required ratio of foaming expansion.
2. Description of the Prior Art
A polyorganosiloxane foam is widely used as heat-resistant shock absorbers, insulating materials, gaskets or the like by virtue of its excellent heat resistance, flexibility at lower temperatures, ozone resistance and ultraviolet light resistance. Further, as the demand for heat insulation in a building increases recently, it is contemplated to use polyorganosiloxane foams as heat-insulating sealants in spaces between walls of a building since the foams exhibit an excellent weather resistance, heat resistance and cold resistance, and an extremely small compression set coefficient. Foam forming materials used in these applications are required to have a pot life of at least 5 minutes, preferably about 10 to 20 minutes for the installation work at the job site.
A technique for forming a polyorganosiloxane foam with evolution of hydrogen gas is described for example in Japanese patent publication No. 11839/1970. In the method disclosed in this publication, a composition containing as effective constituents a silicon compound having an aminoxy group bonded to a silicon atom, a polydiorganosiloxane having a terminal blocked by silanol group, and a silicon compound having a silicon-hydrogen bond. Foaming is made by hydrogen gas evolved when hydroxylamine formed by the curing reaction of the silicon compound containing an aminoxy group with the polydiorganosiloxane end-blocked by silanol group reacts with the silicon-hydrogen bond. In this method, foaming starts when the above-described three effective constituents are mixed together. However, when it is intended to obtain a sufficient pot life, i.e. the time elapsing between mixing and start of foaming and viscosity increase, the foaming reaction passes through its peak before the generated foam reaches a cured state exhibiting the foam breakage preventing effect. Therefore, the required ratio of foaming expansion cannot be obtained. Conversely, when curing is promoted to develop the foam breakage preventing effect before the foaming reaction reaches its peak for the purpose of increasing the ratio of foaming expansion, foaming and viscosity increase start prematurely during mixing or application work. Accordingly, this method is disadvantageous in that the pot life must be set to only one or two minutes and that the obtained foam exhibits insufficient ratio of foaming expansion and insufficient properties.
In the formation of a polyorganosiloxane foam, it is important that the composition has some viscosity and exhibits the foam breakage preventing effect so as to prevent bubbles formed by the evolution of hydrogen gas from breaking. Namely, a required ratio of foaming expansion can be obtained only when the foaming speed is well balanced with the viscosity increase and curing speeds. However, in the above-mentioned prior art, the viscosity of the composition does not increase at the beginning of foaming to such an extent that the foam breakage preventing effect develops effectively. This results in foam breaking and a low ratio of foaming expansion.
The present invention eliminates the above-mentioned disadvantages of the conventional organosiloxane foam.